Early indicators of risk become increasingly relevant to alcohol and other drug use (substance use; SU) in late adolescence when SU escalates and substance-related problems emerge. Risk for SU builds cumulatively and sequentially over the course of adolescence, and understanding SU in late adolescence requires a characterization of the early adolescent risk context. Behavior problems in early adolescence set the stage for poor adaptation and increased risk for SU with incentive salience and effortful regulation playing an important role in escalation of SU. Yet, most research has focused exclusively on risk conferred by externalizing problems (e.g., aggression and delinquency). The etiological role of internalizing problems (e.g., anxiety and depression), though potentially significant, is poorly understood. No long-term longitudinal studies have followed youth from pre-initiation to use, escalation, and emergence of problems to provide a developmental account of the link between internalizing problems and SU. Moreover, social context (e.g. peers, parents) is a strong influence on adolescent SU, and changes dramatically from early to late adolescence. Limited SU research has focused on individual level changes in internalizing problems within this social context. The proposed project fills these critical gaps in the literature. This is a continuation o a study of SU in a community sample initially assessed at ages 11-13 years. The proposed project will follow the sample into late adolescence for three additional multi-method assessments (mean ages 18, 19, and 20 years) to evaluate continuity and discontinuity in individual and environmental risk over these years. A critical feature of our longitudinal design i the ability to compare directly how the role of internalizing problems, mediation, moderation, and potential bidirectional associations shift across age and stage of use (initiation, heavy use, problem use). The project will examine: 1) The changing role of internalizing problems with age and stage of use; 2. Key mediators (motives for SU and peer affiliations) and moderators (peer norms, parent-adolescent relationship quality) of the effects of internalizing; 3) Reciprocal associations between incentive salience, effortful regulation, internalizing symptoms, and SU.